Extraction and recovery processes are common, for example in water purification, mining, and waste treatment. While the specific unit operations and process chemistries may be different for these processes, the basic approach is the same—elaborate mechanical and chemical processes which are usually lengthy, energy intensive, and expensive. Many of these processes utilize, at least in part, absorbents such as activated carbon or ion exchange absorbents to remove or sequester dissolved species.
Carbon, particularly activated carbon, is a common absorbent, but is relatively nonspecific. Molecularly imprinted polymers (“MIPs”) have been developed with substantially improved specificity for a “target” molecule which would be desirable to remove from a process stream (e.g., in waste treatment applications) or to sequester (e.g., isolate) from a process stream because of its value. MIPs are polymers designed to be highly selective for a specific target molecule. MIPs are prepared by polymerizing a polymerizable ligand which coordinates or “binds” to the target molecule. The target molecule and the polymerizable ligand are incorporated into a pre-polymerization mixture, allowed to form a complex, then polymerized (typically in the presence of one or more non-ligand monomers and a cross-linking monomer). The target molecule thus acts as a “template” to define a cavity or absorption site within the polymerized matrix which is specific to the target molecule (e.g., has a shape or size corresponding to the target molecule). The target molecule is then removed from the MIP prior to its use as an absorbent.
However, while highly selective to the desired target molecule, MIPs have significant drawbacks. For example, if the target molecule is highly valuable (e.g. a precious metal) or hazardous (e.g., toxic or radioactive), the need to use the target molecule itself as a template in preparing the MIP can be prohibitively expensive due to e.g., the cost of the target molecule or the precautions required to handle the target molecule compared to less selective, but far cheaper absorbants. In addition, because the target molecule must remain complexed to the polymerizable ligand during the polymer synthesis, if the target molecule/polymerizable ligand complex is unstable or otherwise incompatible with the polymerization conditions (e.g., catalyst, other monomers, low solubility, etc.) it may not be possible to prepare the MIP at all, or require complex or difficult reaction conditions. Accordingly, it would be desirable to prepare absorbents with the advantageous selectivity and other characteristics of conventional MIP materials, but without the disadvantages inherent in using the target molecule as a template in preparing the MIP. The methods and materials of the present disclosure provide such improvements over conventional MIP materials and processes.